System for determining the position or path of an object in space



ay 24, 94. P. w. NOSKER 2,4%787 SYSTEM FOR DETERMINING THE POSITION ORPATH OF OBJECTS IN SPACE 4 Sheets-Sheet l Filed May 4, 1944 ,0555/3 Vl?770A/ 5l 5 cow-f0.1, 53

'SWW/N INVENTOR Filed May 4, 1944 P. W. NOSKER SYSTEM FOR DETERMININGTHE POSITION OR PATH OF OBJECTS IN SPACE omEEvHr/ofv amr/mf 4Sheetsj-Sheet 2 H/RFXHNE @ECE/VER slm/m. gemeen@ PAUL ,144 /VlosrE/c?May 24? 1949. P. w. NOSKER 25,47%78? SYSTEM FOR DETERMINING THE POSITIONOR PATH OF OBJECTS IN SPACE 4 Sheets-Sheet 3 Filed May 4, 194A BY l/Wgz' v tg N ATTORNEYJ I May 24, ww. P. w. NOSKER 2,479,737

SYSTEM FOR DETERMINING THE POSITION OR PATH OF OBJECTS IN SPACE FiledMay 4, 1944 4 Sheets-Sheet 4 l 'The invention describe factured and.used by'orfor the.Government-forg. governmental purposes, without the4payment-to Fig. 3 is a diagram of vequipment'used in practicingthe'invention gefangen-ily 24,1949" fQRiPMH 0F AN OBJECT. rs-sence me ofany'roya1ty1thereom This invention relates Ato a method of andalpparatus -for determining the position' ory path Aof herein may bev.manu-1.

an object in space. e. g' an ,airplane injight. An object of theinventionifis tolprovidea method of directly and rapidly measuring thedis'-l -tance between two points.l one ofwhich mayAv be moving,without'einploying conventional measurv ing instruments'.- A partic'ularobject. is'to pro-A vide a method which facilitates the deteri'nina-V'tion-of the altitude, vtru'e speed, ground speed,

` vrate of climb, resultant acceleration, tangential acceleration andfradialacceleration of an. airplane in '-ight. The-.invention couldalso, be emlf' ployed with rocketbombs, targetfairplanes, modelairplanes,` weather observation balloons, radiol controlled aerialtorpedoes, -and other objectswhether travelingthrougnthe airl or fixed.`Further objects and advantages will beapparent from the followingdescription of five arrange- 'ments of apparatus for practicing themethod.

The Paul J Holmes Patent No. 2,198,113, dated April 23,l 1940, disclosesa' navigation method which is somewhat like the one I propose, but thereare many diierences, the most important and fundamentaldiiference'beingthat the patentee determines not` the positionv in three-'dimen-4bedetermined at any time by radio Wave measure- 'i Now referring toFig-3, one ofthe observation l y stations, for examplefSI', is shown ascomprising *f sional space but only the-two-d'imensionalpositionrelative to the ground, or inthe phrasing of 'thepatent, by horizontalazimuth and distance ironia known point. The vreason for this is thatthe patentee de'siredto make it possible to-follow.

von a special radio range map the course ofthe airplane relativel tostations o n the ground. Patents No. 2,134,716, dated November 1, 1938,

a'diagramflke Fi simplified by. the-'employment ofvland'lines; v.

Fig. 'isanother diagram of's'till anotlfierarf 1 rangement ofapparatus;v and Fig. '7 isI still l another diagram of apparatusforpracticing' the'f ginvention. .'1- l y Referring particularly 'tojg thev"drawings, 'andl f first to Fig. 1, thepositinand'pathof airplaneA- yin fight is to be determinedifrom measurements taken at three stationsSI;fS2, andlS3, whichffor -convenience are as sumed'as located ontheearthssurface, at known distances from each other-'but not inthe samestraight line.'A The straight'line joining-'Sf'with A, is designated DIthe straight line'ljoining S2 with A'is designated D2;A andthe linejoiningS3- with A is D3.` 'Il'iese 'three distances, DI, D2, andDanormal'ly are 'eachchangingA constantly while the airplane vAinflight. Ordinarily thev airplane `will not be observable from allthre'evst'ations, and it may notbefobservf l able .from any; yet. itsinstantaneous position may ments taken at the three stations,and from'a-traced'and its kinematics determined.,

a constant-frequency signal vgenerator I I, coupled by leads I2 toaradiol transmitter `I3 coupled to an antenna I4. The constant-frequencysignal generated by generator I-Iis caused to modulate a radio-frequencycarrier wave "generatedgby vtransmitter I3, and the modulated Awaveis^radi and No. 1,750,668,- dated March 18, 1930, are other examplesfrom .the prior art, eachqhaving a re mote bearing on the inventionhereinv described. In the accompanying vdrawings 'showing schematicallyseveral practicable arrangements of apparatus Afor practicing theinvention, v v

Fig. lis a diagram of a plurality of observaated by the antenna I4' intospace.

- and an lantenna I9 connected with transmitter tion stations and anairplane whose position or explained; Fig. 2 is a diagram lines for saidequations, and showing a dieren't arrangement of stations;

like i'bueomietmg'the one formv of vradiouwalve'f Y wave transmittedfromthe airplanestation isre-f r ceived by antenna 2|)` and transmittedtoradio re-` I8; -Part of the modulated wave radiated'by antenna I4 isreceived by antenna I6 and demodulated by receiver I5, whose signalouput is im'- course is to'be determined, with lines for the X,':pressed upon vtransmitter I8. This eiectsvmodu Y, and Z'axes, andother'lines to aidin deriving' certain mathematical equations, ashereinafter' lation of another radio frequency carrier wave thatradiatedvv by anetnnay I4. The modulated ceiver 2I,`Where' itisdemodulated. Thevsignal output from receiver 2l, is transmitted by leads22 Fig. Akil-is' a ydiagram showing- Il the preferrevd-far-yrangerrieni'of equipment; i v g .'4 .butsomei'lhatv The other twostations S2,` S3 are exactly the same, hence are not shown. vTheairplane or other object 3 to filter network 23 where al1 components ofthe modulation are removed except that corresponding to theconstant-frequency signal generated by generator I l. Leads 24 connectthe filter network to the responsive element of a phase angle meter 25,coupled by leads 28, 29 to the leads I2 which connect the signalgenerator lI I and transmitter I3.' Because of this manner ofconnection', the phase meter measures the phase of the output signalfrom the iilter network with respect to the output signal from thesignal generator. The reading of the phase angle meter is then afunction of the total phase change occurring throughout the transit ofthe original signal to the airplane A and back again. This phase changeis composed of two separate parts, one of which is constant due to thefixed characteristics of the transmitter I3, receiver I4, transmitterI8, receiver 2l and lter network 23, and the other of which is variablein direct proportion to the total distance between the observationstation and the airplane. If the phase angle meter is setto zero whenthe airplane is at or very near the observation station, subsequentreadings on said meter when the airplane is in night are indicative ofthe distance between the observation station and the airplane.

To express mathematically the relationship between the phase angle shownby meter 25 and the distance DI, D2, or D3 between stations SI, S2, orS3, respectively, and the airplane, the following symbols will beemployed:

D=distance to be measured (may be DI, D2

or D3) P=phase angle shown by the meter 25 Pn=phase angle when theairplane is at the station and D=O V=speed of radio-frequency carrierwave in space =modulation frequency L=modulation wave length on thecarrier wave in space Now the total phase difference between two pointson a wave is proportional to the number of wave lengths by which thosepoints are separated, and a separation of one wave length is equivalentto one complete phase cycle or 2 1r radians. In this particular case,the equivalent distance between the two points whose phases are to becompared is twice the actual distance between the two stationsconcerned, because the wave is required to traverse the path to and fromthe re-transmitting station.

Therefore,

However, the initial adjustment of the phase angle meter can be made toset Po=0, in which case or transposing,

4 Inserting the value of L from Equation 3 in Equation 2 gives V D-a-FP(4) 5 The speed, V, is an accurately known constant,

and theanodulation frequency, F, may be measured directly byl well knownmeans.` Thus the constant of proportionality between D and P may beevaluated, and the scale of the phase angle meter may be graduateddirectly in units Yof length.

Any one of the distances DI, D2 or D3 is measured by use of Equation 4.However, the signal frequencies employed for the three differentmeasurements are necessarily unequal, to permit proper separation of thesignals by the three different-lter` networks 23 at the three stationsSI, S2, S3.

Alternatively, three dillerent radio-frequency carrier waves could beemployed at the three stations, with one signal frequency, but as thiswould necessitate three different receiver-transmitter-antenna hook-ups`on the` airplane, it would normally be` considered anundesirablearrangement. The preferred apparatus at the airplane station comprisesmerely the parts shown in Fig. 3, which may be standard equipment onairplanes equipped to receive and send messages by radio.

Referring to Fig. 1 again, station SI is arbitrarily placed at theorigin of the X, Y, Z axes, with station S2 on the Y axis and station`S3on the X axis. This placement is not mandatory but is convenient forpurposes of description. The X and Y axes are in the planefof thesurface of the earth, while the Z axis is perpendicular to said plane.Directly beneath the airplane A is a point Alfwhich is in said plane,being separated from the airplane by a distance equal to vertical linee, from station SI by a distance 1*, from station S2 by a distance m,and from station S3 by a distance n. Point AI is also a certain distance:c from the Y axis, and a distance y `from the X axis, lines :c and ybeing of course in the plane of the VX--Y axes. From Fig. 1 thefollowing equations are apparent:

For convenience, the distance from station Sl to station S2 equals thedistance from SI to S3, and such distance is designated d, in thefollowing presentation:

e a e dt di dt 76 also thesecond derivatives.

' the true speed in space avons? From these time 'ratesof change, it ispossible to express the rate oi climb i dt the ground speed The phaseangle meters could be used as simple 4 indicating devices from whichreadings could be-l taken visually at desired intervals o f time, butpreferably their indications will be recorded by means of a motionpicture camera (not shown) orfsome other graphic device that records ona strip of paper or chart the time of recording as well as -the actualreading. To facilitate recording, the phase meter preferably is of atype that lyields a direct-current output proportional to the phaseangle. The circuits of the preferred type of phase meterfalso details ofits construction, are omitted because no claim is made thereto.

The above description explains one method of lpracticing the invention.An improved system of measurement, now preferred by me because of itssimplicity. utilizes only one modulation-frequency for measurement ofthe three distances DI, D2, D3. See Fig. 4. A radio wave modulated witha single and constant frequency is trans'- mitted from station SI and isreceived at the airplane station, where the modulation is detected andthen retransmitted on another radio Wave having a differentconstant-frequency. This radio wave is received at stations SI, S2, andS3, and the modulation as received at stations S2. and S3 is relayed tothe central or control station SI by conducting lines or byre-transmis'sion on two different radio carrier waves. Finally, thephase angle of each of the three returning i pled Yto the vthreereceivers as shown. All three phase meters are connected to leads I2,yas in the arrangement of Fig. 3. f

To illustrate the manner in which the three phase anglemeasurements maybe employed to .determine the required straight line distances DI,

.D2,\D3 to the airplane, 'the following symbolsv maybeused:

Pigphase angle at BIA of modulation received at l s--phase angle at 'SIof modulation received at Plfphase angle at SI of'modulationl receivedat Now the actual path traversed by the modulation received-at SI is thesame as in the rst described arrangement and is equal to 2DI. RewritingEquation 4, we obtain:

f 4 F. P1= D1 (17) provided the equipment is initially adjusted tocounteract all constant phase shifts in the system due to thecharacteristics oi' the equipment involved. The total path traversedbythe modulation received at S2 isequal to the sum 'of DI,

D2 and d; hence (D14-D244) (1s) yBut the distance d is iixed andproduces a constant phase shift which may be counteracted when theinitial adjustment is made tov eliminate other constant phase shiftsoccurring in the various elements of the system. When this initialadjustment has been accomplished, the value of P2 is:

modulation signals is measured at station SI with t respect to theoutgoing modulation signal being ytransmitted from that station. Thisarrangeprises a single radio transmitter I3 and antenna I4 for radiatingamodulated-frequency wave, the modulation being on a constant-frequencywave generated by signal generator I'I. The airplane station is the sameas in Fig. 3, namely, a receiver I5 with antenna I8 coupled to atransmitter I8 with an antenna I3'. Two of the ob servation stations, S2and S3, are similar tothe airplane station, since they each comprisemerely receivers Ia and I5b, with antennas I6a', I3h respectively,transmitters Ilia, I8b, and antennas i3d, l3b respectively. ReceiversI5a, |517 are each tuned to receive signals from transmitter I3 andtransmitters I8a, I8b are preferably each tuned to differentfrequencies, and to frequencies different from those of transmitters I3and I8.-

three phase meters 25, 25a, 25h individually cou` P2= (2;).(D1+D2) (19)Similarly, the modulation received at-S3 must traverse a total pathequal in length to the sum of DI, D3and d. After the same initialadjustments have been made:

P3= lwi+b (zo) Simultaneous solution of Equationsv 17, 19 and 20, yieldsthe following values for the three required distances:

The initial phase adjustments mentioned above may be accomplishedconveniently by placing the airplane on the ground at a point A2(Fig. 1) spaced from stations SI, S2', S3 by the known distances a, band c, respectively. Then with the complete flight path recording systemin operation, the three phase meters at stations Si, S2. S3 will beadjusted to the proper initial indications which are dened by thefollowing expres- V l sions: 4

4x'F` S1 adJustmentaT-a (24) s2 diuament-i'fwb) ('25) sa edjusmentngiaw)v (26) This initial adjustment could befacilitated in Thepreferredarrangement fs connection witlir permanently established sta'- ltionsSI., S2, S3 near an airport by'placing a fixed f marker anywhere on thefield aty an accurately f knownlocation. f Immediately prior to thestart of a night which is to berecorded, the airplaney could he taxiedyto the marker and the three inif y,tial phase meter adjustmentscouldthenkrbe made at the recording station' Sl. f

This preferred varrangement yis advantageous i over the onerst'fdescribed in that (1) only one modulation frequencyis required; (2)transmisi f sion 'of a radio wave to the'airplan'e is required i yfromonestation only; `(3) no selective filtering of separate components ofafcomplex module-iy tion signal is required; (4) the total investment fin apparatusy (hence ymaintenance costs etc.) is

less. 4, f f f of Fig. 4y may be further simplified as illustrated inFig. :5, wherein ,like parts are identified by; like reference :nu-

merals. In Fig. 5, two ofy the receivers. at the f f control station areeliminated, rbeing unnecessary because a transmitter at each of theobservation f stations is not used. ,'Instead, each observation stationis .directlyy connected by leads 4i, 42

. (whlchare land lines. e. g., itelephoneflwires) with f tweengeneration andtiinal receptionof indii yvidual pulses is ydeterminedbymeans ofv a timing.

device 40 that is connected vbetweenitlzie output of the pulse generatorf 8 lr and the output of the radio receiver-38 at ther observationstation. This timing device may be electronic inicharacteriand' i f itis preferably'one having :tast response and high inherent stability.Since a phase angle meter is also a time-measuring device. I have usedthis i f term in some' of lthe claims to designate either' timing deviceInfor ar phase angle meter.

As in the system rusing modulation on a con-i f -f tinuous radio wave,time delays of fixed amount` will: occur in the various devices requiredfor'r f v transmission, reception.'retransmission,. and re'- f f turnreception 'of the pulse signals. However,

f such constant delays may be accounted for by a corresponding phaseangle ymeter at .the con,-r

troly station. This arrangement, while employsidered disadvantageousinthatiland lines must be usedto transmit electrical impulses .to measurethey phase angles of the modulated waves received at the two observationstations.

f yThe basic method of this invention has been that wave.An'alternativemethod, which rallows f the measurement of distanceandlocation by the between successive pulses ymay be long comparedy to theactual duration vof an individual pulse. These electrical signals areradiated into space by antenna 32. A radio receiver 33 on the airplane,coupled to anantennaii, responds to the radiated energy from theobservation station and yields at its output terminals short pulsessimilar to those produced by thepulse generator. These pulses in thereceiverfoutput actuate a'keying device 35 which controls a transmitter3B. on the airplane in such a manner Vas to produce pulses similar tothose` radiated from the observation station. These pulses are radiatedby antenna 31. In the case with modulated continuous waves, the`carrier-frequencies of the two radio trans.

. mitters 3U and 3B preferably are different; however, this 4pulsesystem may readily employ one single radio-frequency for both of thetranslmitters 30 and 36. A radio receiver 38 at the observation stationhaving antenna '39 responds to the pulses radiated from the airplanestation f "and thereby produces fin its' .output circuit pulse signalsthat are similar to those originating at the pulse generator 3l butlthatdoccur at later times because of the delays in transmission bef ingless apparatus, in some ycases will :be ycon methods similar ito thosel'iereinbefore` described. and the variable time delays l,may thuszb'erecogey ynized yandrfemployed to define the changngdis.' tances to bemeasured.y f f f f f rWhile the method'ofthefinvention'is'especially fuseful in ydetermining the path of an airplane'in y flight. it could beused to'estahlishy the location oii any land or water-borne object thatlis equipped to receive and 11e-transmit the necessary signalsvObviously. the reverse of the described arrange@ vment might beemployed,y i.l e., the signal generate: lng and; phase angle measuringyapparatus might ybe on the movable object to permit the navigatorofthat object to determine the position, thereof withrespectto:re-transmitting stations' at known locations.

. In the arrangements so far'described, one or,

more of the observation stations is a control stas tion, withtransmitting,,receivingand'measuring f i apparatus at the controlstation. lFig.y 2 shows a .diiierent arrangement, wherein the controlstation is neither ony the X or Y axes nor at ythe;r f

origin, but is at any point Cin the plane of 'the X--Y axes. Theairplane A is anywhere above the surface of the earthand has a stationlike the one shown in Fig. 3, or like that of Fig. 6 if preferred. Thetransmitting equipment is not located at observation stations SI, S2,S3,`or the control station C, but is at a relatively remote point T.Modulated-frequency waves or pulses areV radiated at point T; and arereceived at the airplane station, also at the control station. 'I'hosereceived at the airplane station are re; transmitted to the threestations SI, S2, and S3, and by means of electrical circuits (as in Fig.5) or radio transmitters (as in Fig. 4), are relayed `to the controlstation. With this arrangement',

the "observation' stations are nothing more than receiving and relayingpoints and work entirely f automatically. The controlV station will haveat least four radio receivers,- or the equivalent, to permitmeasurements of the time lags between the waves or pulses receiveddirect from the transmitting station T and those re-transmitted from theairplane `to the relay stations, thence to `the control station. In Fig.7 I show `another arrangement of api paratus which is similar to Fig. 3except that the two R. F. receivers do not include means foi'demodulating the incoming radio-frequency waves. Instead, each receiverdelivers at, its out?.

.tween the..-two stations.,- -.-;The timeintervalbe- .22.5

put side a signal which is merely an amplified re'- production of theparticular radio-frequency antenna signal to which the receiver istuned.,. 4 l In further Vexplanation of the system of Fig. "Z, let usassume that the signal delivered by signal generator E0latthercontrolstationlis applied to R. F. transmitter so as to producemodulations of the R. F. carrier wave radiated from the antenna 52. Thismodulated carrier wave is received by antenna 53 at the airplanestation, and after passing through R. F. receiver 54 is amplified andthen changed in frequency by a constant factor by frequency changer 55.Thus v no demodulation takes place atv the airplane station. The newcarrier wave thus created, retaining the original modulation, is thenpassed through R. F. transmitter 56 and is radiated by antenna 51,received by antenna 58 at the control station, 'and after amplificationby R. F. receiver 59, is demodulated by demodulator 60. The modulationsignal thus obtained is then com'- pared with the corresponding signalat the output side of signal generator 50, by means of phase ,meter 6I,which therefore gives a measurement of time or phase diiierence and maybe calibrated in units of length to give readings of the distance of theairplane from the control station.

The system of Fig. 7 is applicable to the complete three-dimensionalpath-determining methods described above in connection with Figs. 4

and 5. With the arrangement of Fig. 4, each observation station would belike the airplanel station of Fig. 7 and the carrier frequency wouldthus undergo one change at the airplane station -and another change ateach of the observation equivalent4 to timer 40. The method of Fig. 7

has a practical ladvantage in that the absence of demodulation, exceptat the receiving side of the control station, Jminimizes the chances of10 night. These statements indicate that the invention may be veryuseful in experimental work with airplane models as well as withfull-sized airplanes, for instance in divetesting. Still anotheradvantage is that speeds may be measured at speeds above those at `whichconventional pressure instruments are reliable, up to and above thespeed of sound.

, The present invention accomplishes the dete mination not only of thehorizontal positionfof a moving object but also of the vertical distancefrom that object to the reference plane. Thus this invention permits thelocation of an object in terms of three-dimensional co-ordinates inspace.

A -further important advantage of this method of position and pathrecording is that it is relsponsive only to objects equipped withsuitable apparatus that is in operation and adjusted to cooperate .withsimilar equipment located at the several observation stations. Unlikemethods dependent upon reection of radiant energy, the present method ofposition 'measurement is unaffected by the presence of other objectssimilar to the one under observation, even when those other objects arenear to the one being observed. Obviously the method is not limited touse of the apparatus that is shown herein for the purpose ofillustration.

What I claim is:

1. Means for continuously obtaining information sucient to determine theinstantaneous errordue to phase changes of the modulation signal inresponse to temperature effects or other phenomena unrelated to the.distance being measured.

Assuming that the apparatus is properly installed and has suillcientpower, the method of the invention accomplishes the direct measurementof the distance between two isolated points equipped with the apparatus.No instruments of the light-ray type are used, hence the vmethod --worksas well, or better, in total darkness than in position of an airplanewith respect to three ground points located at the vertices of atriangle,

said means comprising a control station located at the iirst of saidground points, said control station comprising a local oscillator andmeans for radiating a first carrier wave modulated by the frequencyofsaid local oscillator, means'in said means at said control station forreceiving and demodulating said second carrier wave and for comparingthe phase of the resulting signal with that of the local oscillatorsignal, means at the second of said ground points for receiving anddemodulating said second carrier wave and for modulating a third carrierwave with the signal resulting froml demodulation of said second carrierwave, means at saidl second ground point for mination of true speed,ground speed, altitude.

' rate of climb. acceleration, andvother kinematic functions, withoutreference to any characteristics .Y

of the airplane or of the atmosphere. Another free from lag. Stillanother advantage is that airplane, forexample oi an experimental type,

which is deliberately or accidentallyv destroyed in feature-is that theinventive method is inherently a crash.- The methodl will revealdiscontinuities in a flight path, hence will identify the point ofoccurrence of,"and the kinematic conditions at-v tending, anydistinte'gration of an. airplane radiating said vmodulated third carrierWave,

meansat the third ground point for receiving and r demodulatmg saidsecond carrier wave and for modulating a fourth-carrier wave with thesignal resulting from demodulation of said second carrier wave, means atsaid third ground point for radlating said modulated fourth carrierwave, means at said control station for receiving-and demodullating said.third carrier wave and for comparingthe phase of the resultingsignalwith that of the local oscillator'signal, and means at said controlstation for receiving and demodulating said fourth carrier wave and forcomparing the phase of thevresulting signal with that of the localoscillator signal.

- 2. Means for continuously obtaining information suiiicient todetermine the instantaneous position of an airplane with respect tothree ground points located at the vertices of a triangle,

said means comprising a controlstation located at the rst of said groundpoints, said control station comprising a local oscillator and means forradiating a lrst carrier wave modulated by l 11 the frequency of-saidlocal oscillator, means in said airplane for receiving said modulatedfirst carrier wave and for changing the frequency thereof withoutaltering the modulation frequency to produce a second carrier wavehaving the same modulation as said first carrier wave, means in saidairplane for radiating said second modulated carrier wave, means at thesecond of said ground points for receiving said second modulated carrierwave and for changing the frequency thereof without altering themodulation frequency to produce a third carrier wave having the samemodulation as said second modulated carrier wave, means at said secondground point :for radiating said third modulated carrier wave, means atthe third of said ground points for receiving said second modulatedcarrier Wave and for changing the frequency thereof without altering themodulation frequency toproduce a fourth carrier wave having the samemodulation as said second carrier wave, means at said third ground pointfor radiating said fourth modulated carrier wave, means at said controlstation for receiving and demodulating said second carrier wave and forcomparing the phase of the resulting signal with that of the localoscillator signal. means at said control station for receiving and-demodulating said third carrier wave and for comparing the phase of theresulting signal with that of said local oscillator signal, and means atsaid control station for receiving and demodulating said fourth carrierwave and for comparing the phase of the resulting signal with that ofsaid local oscillator signal.

i PAUL W. NOSKER.

REFERENCES CITED The following references are of record in the file ofthis patent:

UNITED STATES PATENTS Number Name Date 1,750,668 Green Mar. 18, 19301,945,952 Nicolson Feb. 6, 1934 2,134,716 Gunn Nov. 1, 1938 2,198,113Holmes Apr. 23, 1940` 2,207,267 Plaistowe July 9, 1940 2,248,727 StrobelJuly 8, 1941 2,406,953 Lewis Sept. 3, 1946 2,408,048 Deloralne et alSept. 24, 1946 FOREIGN PATENTS Number Country Date u 116,666 AustraliaOct. 10, 1941. 116,667 Australia Oct. 10, 194i.

